Fluid Filter

ABSTRACT

A fluid filter comprises a filter housing, having an inlet end ( 202 ) and an outlet end ( 204 ), and a plurality of bundles of fibres ( 211 ) extending longitudinally of the housing and being secured at the inlet end. The fibres are charged with an electric or magnetic field to selectively block or allow the passage of particles of a known charge present in the fluid through to the outlet end. To flush the filtered particles out of the filter, the charge imparted to the fibres is reversible to allow the charged particles to flow freely through the filter. The filter can also be used to control the settling characteristics of particles in a fluid.

The present invention relates to a fluid filter, and particularly although not exclusively to a high pressure and throughput filter for removing solid material from a liquid such as water.

A filter which makes use of fibres to trap material entrained within the medium is disclosed in U.S. Pat. No. 5,470,470 and U.S. Pat. No. 4,617,120. A similar device is disclosed in EP-A-0280052.

The principle of operation of the device of EP-A-0280052 is shown schematically in FIGS. 1 and 1 a. The filter 100 comprises a filter housing 101 with an inlet end 102 and an outlet end 103. Extending longitudinally of the housing is a plurality of parallel fibres, held in place by a support 106. Surrounding the fibres is a flexible waterproof membrane 104.

During filtration, the membrane 104 is pressurised as shown at 107 in FIG. 1 a, thereby compressing the fibres towards an internal pinch point 108. The material to be filtered is forced through the filter in the direction shown by the arrow. The filter may be flushed and cleaned by releasing the pressure within the membrane and back-flushing in the opposite direction to the normal flow of filtration.

In one particular embodiment, EP-A-0280052 discloses a distensible balloon with fibres surrounding it, so that as the balloon is distended the fibres get pushed out against the internal circumference of the filter housing.

Whilst this form of filtration by compression of fibres may be effective at filtering out particles of a certain size or above, it cannot distinguish between particles of different material but of the same size. Thus the filter cannot be used to separate out different materials unless there is a definite difference in the particle size of each material. For example, it may be desirable to remove salt from a fluid but to leave certain other minerals in the fluid. Alternatively, one may wish to filter out viruses but to leave in bacteria. Bacteria are larger than viruses, so a filter based on size only cannot achieve this aim.

According to a first aspect of the invention, there is provided a filter for a fluid, comprising a filter housing having an inlet end and an outlet end, and a plurality of fibres extending longitudinally of the housing and being secured at the inlet end, wherein the fibres are charged to selectively block or allow the passage of particles of a known charge present in the fluid through to the outlet end

According to a second aspect of the invention, there is provided a method of operating a filter for a fluid, the filter having a filter housing with a first end and a second end, and a plurality of fibres extending longitudinally of the housing and being secured at the first end; the method comprising selecting a direction of charge to be applied to the fibres to block the passage of particles of a pre-determined charge from the first end to the second end, imparting the charge to the fibres and passing a fluid to be filtered from the first end to the second end.

It is further desired to utilise the filter to charge particles in a fluid as they pass through the filter, for capture or control later. For example, the drinking water in certain countries is a brown colour, albeit perfectly safe to drink. Its aesthetic characteristics are off-putting to the consumer, and it is therefore desirable to be able to alter these characteristics such that the water is clear and appealing to the consumer.

It is therefore a further aim of the present invention to alleviate this problem in a simple yet effective manner.

According to a third aspect of the invention, there is provided a altering the a method of altering the settling characteristics of particles in a fluid using a filter, the filter having a filter housing with a first end and a second end, and a plurality of fibres extending longitudinally of the housing and being secured at the first end; the method comprising imparting a predetermined charge to the fibres, the charge being selected based upon the charge of certain particles in the fluid, passing a fluid whose settling characteristics are to be altered from the first end to the second end, and allowing the particles to settle in the fluid.

Preferred features and embodiments are set out in the dependent claims.

The invention may be carried into practice in a number of ways, and several specific embodiments will now be described by, way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section through a prior art filter;

FIG. 1 a is a longitudinal section through the filter of FIG. 1 in filtration mode;

FIG. 2 a is a longitudinal section through a first embodiment of the present invention;

FIG. 2 b is a longitudinal section through a second embodiment of the present invention;

FIG. 2 c is a longitudinal section through a third embodiment of the invention;

FIG. 3 is a detailed plan view of the head matrix of each of the embodiments;

FIG. 4 is a longitudinal section through a fourth embodiment of the invention;

FIG. 5 is a longitudinal section through the filter of FIG. 4 in filtration mode;

FIG. 6 is a schematic representation of the blocking and passing capability of the filter of FIGS. 2 a and 2 b;

FIG. 7 is a schematic representation of a fibre anchoring system according to the invention; and

FIG. 8 is a longitudinal section through a fifth embodiment of the invention.

Turning first to FIG. 2 a, there is shown a filter 200 of a first embodiment of the invention. The filter is contained within a cylindrical filter housing 201 the size of which may be selected according to the particular fluid pressures, flow rates or volumes required. Alternatively, the housing could be shaped so that its width tapers towards its distal ends. For example, in a specific application the housing has an external diameter of 315 mm and an internal diameter of 290 mm. The filter housing can be made of any suitable rigid material such as metal or an appropriate plastics material. The housing has an inlet end 202 and an outlet end 203, respectively allowing the filtered medium to ingress to and to egress from the filter.

The inlet end is capped by means of an inlet cap 204 having a plurality of inlet apertures 205. Each of these is supplied by an individual inlet pipe 206, thereby allowing if required for a variety of liquids and/or gases to be supplied in parallel to the filter. Suitable connecting means 207 are provided to couple the inlet pipes to further piping systems (not shown) which furnish the liquids and/or gases to the filter at the required pressure and flow rates.

Adjacent to the inlet end 202 of the housing 201 there is cast an internal securing ring 208. This ring provides a lip upon which a head matrix 209 is securely mounted. It is preferred, although not essential, that the head matrix 209 be capable of being easily removed in order to facilitate maintenance and/or replacement. The volume of the filter housing between the inlet cap 204 and the head matrix 209 defines an inlet chamber 210, within which the incoming liquids and/or gases may mix.

The outlet end 203 of the housing may be left open, or alternatively an exit cap and exit pipes may be provided to direct the outgoing fluid after it has passed through the filter.

Referring now to FIG. 3, the head matrix 209 consists of a removable plate 300, made from any suitable rigid materials (such as metal or a plastics material) having a plurality of apertures spaced around the circumference for the receipt of fibre bundles, one of which is shown at 303. The fibres are secured within a metal anchoring collar 710 as shown in FIG. 7. In use, the collar 710 is placed around the fibre bundle and then crimped as shown in FIG. 7 to secure the fibres together. The ends of the fibres 720 are then melted or fused together to form a solid mass. The anchoring collar can then be placed within the aperture 301 of the head matrix, such that part of the collar abuts a shoulder of the aperture (not shown).

Alternatively, the fibres may be secured in any convenient way within the head matrix, for example by melting together approximately 30 mm of the fibre ends to form a solid mass and then securing that mass by means of cross-struts (not shown) within the aperture 301. Between and surrounding the fibre bundle apertures 301 are a plurality of smaller apertures 302, the purpose of which is to allow for the ingress of fluid through the head matrix. Both types of aperture are preferably spaced at equidistant points around the circumference of the head matrix, so as to provide a generally uniform distribution of fibres and also a generally uniform fluid flow between and through the fibre bundles.

Turning back now to FIG. 2 a, it will be seen that in a filtration chamber 213 below the head matrix the individual fibres 211 of the bundles 301 spread out to form a fairly uniform fibre curtain throughout the housing 201. The fibres extend substantially axially along the length of the filtration chamber 213, and are oriented substantially parallel to the direction of flow through the chamber. In this preferred embodiment, the fibres 211 may be secured at the outlet end 203, rather than being left loose. In this manner, electric current passed through the fibres can flow from one end of the filter to the other. In this embodiment, the lower fibre ends 215 are secured to an outlet matrix head 216 having apertures (not shown) for securing the fibre bundles and further apertures (also not shown) for egress of the filtrate. The outlet matrix head 216 is secured in position in some suitable way, for example by means of a further ring cast on the inside of the filter housing 201. Alternatively, the outlet matrix head 216 could be left loose. In this arrangement the filter could be back flushed.

In an alternative embodiment shown in FIG. 2 b, the ends of the fibres are not secured in any way, and they simply hang loose. This embodiment can be used where the fluid to be filtered is conductive, as the charge can then flow through the fibres and into the liquid. However, if possible it is desired to avoid this embodiment as a coating can build up on the fibres that can affect current flow.

The fibres 211 may be of any suitable dimension and conductive material, but preferably they are made of metal or carbon fibre. In one example, the fibres may have a diameter of between 0.15 mm and 0.5 mm. The fibres may be solid or hollow, and may be of circular, rectangular or any other cross-section. For some applications, it may be advantageous for the fibres to be at least partially elastic, either along or across the fibre length. For such fibres, the desired shape-recovery characteristic may also be chosen according to the required application. The fibres may have a smooth or a rough surface and may if required be coated. Fibre coatings such as Teflon and zinc may be appropriate.

In a further embodiment shown in FIG. 2 c, the fibres are magnetised but no current is passed through them. Magnetisation along the fibres is achieved as shown in FIG. 2 c by placing opposing magnetic poles 240 a, 240 b at each end of the filter so as to impart charge to the fibres in a predetermined polarity. Alternatively, magnetisation across the fibres can be achieved by placing magnets in or near the filter housing and placing a magnet in the centre of the housing with the opposite pole facing radially outwards (not shown).

In use of the embodiment of the filter as shown in FIG. 2 a, an electric current is fed through wires 230 connected to the top of each fibre bundle. The current imparts a predetermined charge to the fibres. Referring to FIG. 6 a, the electric charge through the fibres causes an electrical field, denoted by the reference numeral 650 to build up between the fibres. When a fluid to be filtered is passed through the filter, the electrical field blocks the passage of charged particles 660 flowing in the opposite direction to the electrical field towards which they are directed.

These charged particles will therefore collect within the filter to form a filter cake whilst the remainder of the fluid passes through the filter. When the filter has been in operation for some time, a quantity of filter cake will build up. This may be removed by flushing. In order to flush the filter cake out of the filter, the direction of the charge on the fibres is reversed as shown in FIG. 6 b, such that the previously blocked charged particles can pass freely through the fibres, to be collected.

It will be understood by the skilled person that the charge on the particles in the fluid to be filtered occurs inherently in nature. Some particles will be positively charged, and others negatively charged.

In use of the magnetically charged filter as shown in FIG. 2 c, selected charged particles can be blocked in the same way as with the electric field of FIG. 2 a. The magnetic field generated between the fibres blocks particles of the opposite charge to that present in the filter. In order to flush the filter cake, the poles can be reversed to allow the charged particles to pass through the fibres.

In an alternative use of the filter of FIG. 2 a, 2 b or 2 c, the filter can be used to alter the settling characteristics of particles in a fluid by altering charge of the particles. The magnetic/electric field in the fibres alters the charge in certain particles as the fluid is passed through the filter. The particles can then be collected and separated out merely by being allowed to settle. One example of a use of this method is to alter the settling characteristics of drinking water to improve its appearance. In certain parts of the world, drinking water is brown coloured, even though it is perfectly safe to drink. Normally, the brown coloured particles will not settle in the liquid. The brown coloured particles can be removed by altering the settling characteristics of the water by passing it through the filter and then allowing the water to settle, allowing separation of the particles from the drinking water.

In an alternative embodiment shown in FIGS. 4 a and 4 b, it will be seen that in addition to the fibres, there is secured within the centre of the filtration chamber 213 an elongate balloon or distensible member 212. The balloon is disposed centrally within the chamber and extends substantially axially along the chamber so as to be oriented substantially parallel to the direction of flow through the filter. In a first mode, shown in FIG. 4 a, the balloon is relaxed and accordingly presents little or no obstruction to the free flow of fluid through the filter if the fibres are not charged. Fluid entering through the apertures 302 passes substantially unobstructed between the fibre bundles and between gaps 214 between the individual fibres, before passing out of the outlet. No filtering takes place in this mode, but a van der Waals effect may develop.

When it is desired to start filtering, the balloon 212 is inflated by means of a control fluid (hydraulic or pneumatic) which is supplied along an inlet pipeline 216. Alternatively, the balloon could be filled with materials that are substantially resistive to motion (be it rapid motion or slow motion) such as a powder or particles such as sand. As is shown in the drawing, the pipeline may pass through the head matrix 209, or alternatively (not shown) the pipe may avoid the head matrix by entering from the side or from the outlet end.

In the filtration mode of FIG. 4 b, the distended balloon defines a pinch point 403 consisting of a narrow annular region or area between the perimeter of the balloon and the inner circumference of the housing, where the available flow area is at a minimum. The position of the pinch point 403 defines an upstream section 406 on the inlet section of the pinch point, and a downstream section 407 on the outlet side. Preferably, the shape of the balloon is such that, in its distended state, it is substantially symmetrical about the central longitudinal axis 408 of the chamber. Depending upon the application, the upstream and downstream sections may be mirror images of each other. Alternatively (not shown) the upstream section may define a more rapidly-changing annular area, along the length of the filter, than the downstream section, or vice versa.

In any event, when the filter is in filtration mode, fluid passing through it is exposed to a gradually decreasing annular surface area up until the pinch point 403, and then is exposed to a gradually increasing annular surface area. The gradual nature of the decreasing surface area prior to the pinch point is enhanced by making the balloon 212 stiffer at its ends and softer in the middle so that, as it inflates, it forms a generally ovoid shape.

As the balloon expands, it starts to exert a radial force on the surrounding fibres, forcing the fibres to press together and to press against the rigid wall 201 of the filter housing. This of course reduces the size of the passageways 409 between the fibres.

If the fibres 211 are made of a compressible material, the fibres themselves may start to deform, thereby reducing even further the size of the passageways 409 through which the fluid can pass.

Once the balloon has been expanded to the extent required, the electric or magnetic charge is switched on and the fluid or fluids to be filtered are passed through the filter. Typically, the fluid may comprise water or another liquid mixed with one or more solid particulates of varying sizes. As the water and the particulates pass through the upstream section, the electric or magnetic field combined with the gradually decreasing passageway size causes the particulates to be trapped between the fibres. Particulates of a predetermined charge will become trapped due to the electric/magnetic field 650. Of the remaining particles, larger particulates 410 will be trapped relatively early in the graduated filter, whereas finer particulates 411 will be trapped at a point closer to the pinch point 403. The very finest particles 412 will be trapped just prior to the pinch point.

The tapered and gradual increase in fibre compression within the upstream section prevents the larger particles 410 which are caught in the coarser filter matrix, defined by the upper port of the upstream section, from slipping down. This would of course be undesirable since larger particles which were to move downwards towards the pinch point would tend to reduce the gradual nature of the taper and hence the ability of the filter systematically to separate out particles of differing sizes. In the embodiments of the present invention, the gradual nature of the taper ensures that each fibre is securely held by the fibres which surround it. The fibres in the upstream section cannot “flap around” or move, with the consequence that the trapped particles cannot move either.

Typically, the balloon will be distended by an appropriate amount such that only fluid can pass the pinch point. Of course, however, it will be understood that in some applications it may be perfectly acceptable for very fine particulates to pass the filter, in which case the balloon need not be distended to the same extent. By varying the hydraulic or pneumatic pressure on the line 216, the filter may be adjusted to allow through only particles which are smaller than a desired size.

In a further embodiment shown in FIG. 8, the filter includes two balloons 812 a and 812 b arranged in series along a central axis of the filter. The fibres 811 surround the balloons such that when the balloons are inflated as shown in FIG. 8, they compress the fibres together against the inner wall of the housing. In this manner, more than one filter stage is provided, and the two balloons 812 a and 812 b can be used to filter out two different types of particles based on particle size or on another characteristic.

FIG. 5 schematically shows the flushing process for the embodiment of FIGS. 4 a and 4 b. In order to flush the filter, the electric or magnetic field 650 is reversed, and the pressure within the balloon 212 is released, thereby removing the compressive force from the fibres and allowing them to return to their uncompacted and loose state as shown at 503. As the passages 504 increase in size, the fibres reduce their grip on the filter cake, allowing the cake to be washed through by means of a rinsing medium 505. This could be any suitable cleaning liquid or gas, for example water, steam, or even the medium to be filtered (with included particulates). The rinsing medium 505 is passed through the filter in the same direction that the medium to be filtered was passed through in the filtration mode: that is, the filter is forward-flushed.

In an embodiment of the filter in which both a balloon and the electric or magnetic charge is present, the balloon can be used at low pressure only, so as to promote even flow between fibres and not necessarily to create a high pressure gap between the fibres as with the previous embodiment.

It will be understood that such an embodiment may include one or more balloons placed to surround the fibres as in the prior art, rather than a central balloon as shown in FIGS. 4 a and 4 b.

Appropriate valves 506 and piping 507 may be employed so that the washing medium and the filter cake do not contaminate the filtrate. Upstream and/or downstream pressure sensors 508, 509 may be used to determine when the filter is overly clogged with filter cake, and when it is necessary to carry out the flushing process. The process may be carried out entirely automatically, thereby maximising the time that the filter spends in the filtration mode, so increasing throughput.

As part of the flushing process, ultrasound may be applied to the filter or to the fibres to help the cake shake loose. Also, it may be desired to dry the filter cake before release by means such as generating a vacuum within the filter or passing hot air through it.

It will of course be understood that although the flushing process described above with reference to FIG. 5 will always be carried out in the forward direction, in the alternative embodiment of FIG. 2 a (in which the fibres are anchored at both ends) a backward flush could be used instead or in addition, in each case either with or without releasing the balloon pressure.

The filter of the present invention may be scaled in size as desired according to the volumes to be filtered and/or the application in hand. In one preferred arrangement the filter may be manufactured as a plug-in module, in a variety of different sizes.

Although the filter is shown with its longitudinal axis vertical in the drawings, it will be understood that in some applications the axis may be horizontal. The fluid passing through the filter may be pumped, at high or low pressure, or alternatively may be allowed to pass through the filter entirely by the influence of gravity.

It will be understood that the skilled man will be able to adjust a variety of different parameters, as required according to the particular application in hand. Such adjustable parameters include pressure; temperature; fibre size; fibre length; fibre coating; charge on fibre; magnetic field strength of areas within the housing, fibres or fluid; the manner in which the fibres are anchored; flow volume; filter housing material; type of feed; method of inflating the balloon; balloon taper; flushing materials volumes and pressures; and the addition of gases to the mix.

There are a large number of specific applications which may benefit from the use of a filter according to the present invention. Typical applications might include:

-   1. Filtration for reverse osmosis. -   2. The removal of cement, grit and so on following an industrial     process such as precast concrete. -   3. Separation of coagulated products. -   4. Separation of biological tissue. -   5. Separation of coagulated blood and the like. -   6. Separation of vegetable matter, for example the waste water from     olive oil production. -   7. Reducing the turbidity of water generally, where required for     technical or for legal reasons. -   8. The removal of silt from a liquid/water. -   9. Ballast water. 

1. A filter for a fluid, said filter comprising a filter housing (201) having an inlet end (202) and an outlet end (204), and a plurality of fibres (211) extending longitudinally of the housing and being secured at the inlet end, wherein the fibres are charged to selectively block or allow the passage of particles of a known charge present in the fluid through to the outlet end.
 2. A filter as claimed in claim 1 in which the charge is electric.
 3. A filter as claimed in claim 1 in which the charge is magnetic.
 4. A filter as claimed in claim 1 in which the charge direction is reversible.
 5. A filter as claimed in claim 2 in which the charge is generated along the fibres (211).
 6. A filter as claimed in claim 3 in which the charge is generated across the fibres (211).
 7. A filter as claimed in claim 1, in which the fibres (211) are made of either metal or of carbon fibre.
 8. A filter as claimed in claim 1, further comprising a distensible member (212) which when distended, compresses the fibres against the filter housing (201) to create a graduated filter matrix between the first end (202) and a pinch area (403) between the distensible member and an inner surface of the housing.
 9. A filter as claimed in claim 8 comprising at least two of the distensible members (212, 812) arranged in series along a longitudinal axis of the filter.
 10. A method of operating a filter for a fluid, the filter having a filter housing (201) with a first end (202) and a second end (204), and a plurality of fibres (211) extending longitudinally of the housing and being secured at the first end; the method comprising selecting a direction of charge to be applied to the fibres to block the passage of particles of a predetermined charge from the first end to the second end, imparting the charge to the fibres and passing a fluid to be filtered from the first end to the second end.
 11. A method as claimed in claim 10 in which the charge applied to the fibres (211) is electrical.
 12. A method as claimed in claim 10 in which the charge applied to the fibres (211) is magnetic.
 13. A method as claimed in claim 12 whereby the magnetic charge is applied across the fibres (211).
 14. A method as claimed in claim 11 in which the charge is applied along the fibres (211) by an electric current.
 15. A method as claimed in claim 10 further comprising the step of subsequently reversing the direction of the charge in the fibres (211) to enable the flushing of the blocked particles from the filter.
 16. A method as claimed in claim 10 in which the filter further comprises a distensible member (212) extending along a longitudinal axis of the filter housing, the method further comprising that prior to passing the fluid to be filtered from the first end (202) to the second end, the distensible member is distended to create a uniform flow of the fibres through the filter.
 17. A method as claimed in claim 16 wherein prior to passing the fluid to be filtered from the first end to the second end, the distensible member is further distended to compress the fibres against the housing to create a graduated filter matrix between the first end (202) and a pinch area (403) between the distensible member and an inner surface of the housing.
 18. A method as claimed in claim 17 in which at least two of the distensible members are arranged in series along the longitudinal axis of the filter.
 19. A method as claimed in claim 16 in which the filter further comprises at least one distensible member (212) arranged to surround the fibres such that when distended, the distensible member compresses the fibres against each other, the method further comprising that prior to passing the fluid to be filtered from the first end to the second end, the distensible member is further distended to compress the fibres to create a graduated filter matrix between the first end (202) and a pinch area (403) between the distensible member and the fibres.
 20. A method as claimed in claim 19 in which at least two distensible members are arranged in series along the longitudinal axis of the filter.
 21. A method as claimed in claim 10 in which the fibres are further secured at the outlet end.
 22. A method as claimed in claim 10 in which the fluid to be filtered is charged.
 23. A method as claimed in claim 15 including flushing the filter by releasing distension of the distensible member.
 24. A method of altering the settling characteristics of particles in a fluid using a filter, the filter having a filter housing (201) with a first end (202) and a second end (204), and a plurality of fibres (211) extending longitudinally of the housing and being secured at the first end; the method comprising imparting a pre-determined charge to the fibres, the charge being selected based upon the charge of certain particles in the fluid, passing a fluid whose settling characteristics are to be altered from the first end to the second end, and allowing the particles to settle in the fluid.
 25. A method as claimed in claim 24, further comprising the step of separating the settled particles from the fluid.
 26. A method as claimed in claim 24 or 5 wherein the particles become charged upon passage through the filter.
 27. A method as claimed in claim 24 in which certain particles in the fluid are blocked from passing through the filter by the charge on the fibres.
 28. A method as claimed in claim 24 in which the charge is imparted by an electric current.
 29. A method as claimed in claim 24 in which the charge is imparted by a magnetic field.
 30. A method as claimed in claim 24 in which the fluid is drinking water.
 31. A method as claimed in claim 24 in which the filter is a filter for a fluid, said filter comprising a filter housing (201) having an inlet end (202) and an outlet end (204), and a plurality of fibres (211) extending longitudinally of the housing and being secured at the inlet end, wherein the fibres are charged to selectively block or allow the passage of particles of a known charge present in the fluid through to the outlet end. 